The error output tells you what's wrong. With sufficient knowledge about programming you are able to fix it.
If you get namespace errors you are very likely referring the wrong library or wrong library version. Shvdn has changed over time and maybe that mod (very old as you say) needs an outdated version of shvdn. In this case you need to adapt the code to the new shvdn structure, but as I said, you should know that already.

yes. I already did it, I used the shvdn 2.9.4, but i still getting the error, i changed only a single value in the mod, but I still getting the namespace error, I'm not an advanced developer, I just want to solve a little bug

@hardlevelbr If you are still stuck after doing as ikt suggests then please post the exact error message. Maybe we can help you then. Fixing the code of someone else needs a good amount of experience, especially when it's even decompiled. Jus' sayin'.

@hardlevelbr BTW Shvdn 2 was released on Sep 6, 2015. If the release date of this mod is prior to this date it needs a reference to shvdn 1.x. A change in the major version number (the leftmost one) means there was a breaking change and that could explain the error but as I said, we need better information from your side.
Please read http://semver.org/
Of course having shvdn 1.x in the game folder would conflict with later versions of shvdn. In order to avoid this you need to reference shvdn 2.10.1 and fix all broken changes in the mod by adapting to new namespaces, member names, parameter sets, calls and so on.

One thing I noticed is there's two scripthookdotnet in references in visual studio, but one is marked with some error that I can't figure out, and I already inserted the references, follow some screenshots, if someone could help me I apreciate...

@hardlevelbr Well first of all shvdn should only be referenced once! Remove that erroneous one from the reference list. It casn't be found anyway (that's why it has this yellow triangle with the exclamation mark).
I can't read that error log because it's in spanish language but what I see is that even simple things like missing brackets and semicolons are listed. In other words, that code is a total crap! However those errors are displayed in the code window at design time and should be easy to find (look at the line numbers in the errors list). All this is basic programming knowledge. Are you sure you can handle the task ahead of you?

I know the basic of some languages, actually I'm a frontend web developer, I need this mod to make some videos, but the mod have a bug that make impossible to complete the missions, after the decompilation I could find where I need to change to make it work, it's just one value, but I can't recompile...

It's strange, if the mod is already compiled, why I can't recompile in the same way? Could be some incompatibility with visual studio 2017?

@ikt i'm not removing, only changing a value, it's a distance value, this mod have a bug that make impossible to complete the mission, it spawn a enemy far away but when you try to reach then, in same time is leaving the zone marked in map, when leave the zone the mission is aborted, i'm tryng to change the distance required for the mission fail, the default is 200, i'm changed to 20000, only this... the rest of the mod I didn't any change

@hardlevelbr Since you only want to increase the distance (2 floats) to 20000, why don't you just edit the DLL with a Hex editor?
This should work (assuming you are using the latest version of Gang Mod):
Replace 4 bytes at offset 0x7230 and 0x73B1 with 00 40 9C 46.

@hardlevelbr I thought you were trying to change the behavior of the mod when this thread was just created, but you just want to change 2 values
Probably you can achieve the goal only with the method that Unknown Modder provided, yes.

Most Japanese who upload some mods here don't speak/write English well... Too bad, so sad...